USDA Hardiness Zone 5b
Frost Dates for 61061 — Oregon, Illinois
NOAA 1991–2020 normals from Polo 5NW, IL (856 ft), 14 miles west.
Updated
In Oregon, the last spring frost (32°F) is around April 29 in half of years and has passed by May 14 in nine years out of ten. The first fall frost comes around October 7, as early as September 23 one year in ten, leaving a typical freeze-free season of 161 days (NOAA, Polo 5NW, IL).
- Last spring frost
- April 29
- First fall frost
- October 7
- Growing season
- 161 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- December 1
- Last snow
- March 17
- Winters with snow
- 100%
- Snow per year
- 32.3"
median, 1991–2020
median, 1991–2020
21 of 21 observed
NOAA normal
Frost risk by date in Oregon
Half of springs at Polo 5NW, IL see their last 32°F night by April 29; only one in ten is past it by April 15, and one in ten still has one after May 14. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 9 20%, and after May 14 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 158 Illinois stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 7 in half of years, as early as September 23 one year in ten, and holds off past October 22 one year in ten. A hard freeze of 28°F follows 12 days later, around October 19; in spring the one-in-ten date for 28°F is May 5, 9 days before the 32°F one. The freeze-free season lasts 161 days in a typical year, shorter than at 99% of the 158 Illinois stations; it reaches 180 days one year in ten and falls short of 138 one year in ten. On average 138 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 10 days longer, to about May 9, and return around September 28. Severe cold of 16°F or below comes every winter, usually between November 21 and March 16.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 24 | Apr 29 | May 2 | May 6 | May 9 | May 12 | May 15 | May 19 | May 24 |
| 32°F | Apr 15 | Apr 20 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 5 | May 9 | May 14 |
| 28°F | Apr 4 | Apr 9 | Apr 13 | Apr 16 | Apr 19 | Apr 22 | Apr 25 | Apr 29 | May 5 |
| 24°F | Mar 23 | Mar 30 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 14 | Apr 19 | Apr 25 |
| 20°F | Mar 9 | Mar 15 | Mar 19 | Mar 24 | Mar 28 | Mar 31 | Apr 3 | Apr 6 | Apr 12 |
| 16°F | Mar 1 | Mar 6 | Mar 10 | Mar 13 | Mar 16 | Mar 19 | Mar 24 | Mar 28 | Apr 1 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 14 | Sep 18 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 4 | Oct 6 | Oct 11 |
| 32°F | Sep 23 | Sep 28 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 12 | Oct 16 | Oct 22 |
| 28°F | Oct 3 | Oct 8 | Oct 12 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Nov 1 |
| 24°F | Oct 15 | Oct 21 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 4 | Nov 9 | Nov 15 |
| 20°F | Oct 28 | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 27 |
| 16°F | Nov 5 | Nov 11 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 6 |
Freeze probabilities 1991–2020 at Polo 5NW, IL, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 61061 →Compare Oregon with another place →
Weather by month in Oregon
July is the warmest month at Polo 5NW, IL, averaging 85°F by day and 62°F at night; January is the coldest at 30°F and 13°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 43% of years.
Warmth for growing adds up to 3,067 growing degree days a year (base 50°F), fewer than at 82% of the 158 Illinois stations. 36% of them (1,102) have built up by the end of June, and July adds the most, 715. Precipitation totals 40.1 inches a year, most in June (5.1") and least in January (1.9"); May to September bring 54% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 30 | 13 | 1.9 | 100% | 29 | 0 |
| Feb | 35 | 17 | 2.0 | 100% | 26 | 1 |
| Mar | 48 | 28 | 2.8 | 100% | 22 | 28 |
| Apr | 61 | 38 | 3.9 | 100% | 8 | 103 |
| May | 73 | 49 | 4.7 | 43% | 1 | 355 |
| Jun | 82 | 59 | 5.1 | 0% | 0 | 615 |
| Jul | 85 | 62 | 4.4 | 0% | 0 | 715 |
| Aug | 83 | 59 | 3.7 | 0% | 0 | 651 |
| Sep | 77 | 51 | 3.6 | 27% | 1 | 424 |
| Oct | 64 | 40 | 3.2 | 98% | 7 | 152 |
| Nov | 48 | 29 | 2.7 | 100% | 18 | 21 |
| Dec | 35 | 19 | 2.1 | 100% | 27 | 3 |
Monthly normals 1991–2020 at Polo 5NW, IL (856 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Dixon 1W, IL, 15 miles southwest of Oregon and 196 feet lower, has a last frost 8 days earlier (April 21), a first frost 12 days later (October 19), a season 19 days longer.
When it snows in Oregon, Illinois
The first measurable snow (0.1 inch or more) in Oregon usually arrives around December 1, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Oregon, IL, 0.6 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 43 days after the last snow.
Planting calendar for 61061
| When | What to do |
|---|---|
| February 18 – March 4 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 4 – March 18 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 1 – April 15 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 29 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 15 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 23 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 7 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 61061 is 14 miles from Polo 5NW, IL, which stands at 856 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61061 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.